Support for Child component context

[iravanchi]

A child component context is an implementation of IComposer and IComponentContext that proxies another instance. It first looks up any query in its own repository. If found, the locally found component should be returned. If not, the parent context should be queried.

Any registration or change in variables should be applied to the child context itself, and overrides the parent.

The exact behavior should be defined for methods (such as GetAllComponents).